Three wheeled off-the-road vehicles are provided with relatively wide rear wheels and permit hunters, fishermen and the like to use these vehicles to traverse rugged terrain and to reach remote areas. While such off-the-road vehicles are capable of traversing fairly rugged terrain, they are unable, absent modification, to travel over snow or swamps, owing to the lack of traction and the tendency of the vehicle wheels to sink into the swampy snow or ground.
Attempts have been made to provide conversion units for vehicles such as motorcycles, and even to create specially formed endless track vehicles capable of achieving those ends. These developments have emanated from the early snowmobile, as evidenced by U.S. Pat. No. 2,074,389 to Grant issued Mar. 23, 1937. The snowmobile of that patent constituted a conversion of a standard automobile or truck and involves the replacement of the vehicle front wheels by a pair of runners coupled to the steering wheel mechanism of the vehicle. The rear tires of the truck or automobile are removed, and the rear driving wheels modified to include teeth projecting radially of a disc or wheel and engaging a traction chain which, in turn, is looped about a further auxiliary wheel to a respective side of the vehicle rearward of the automobile or truck drive wheel, so modified. Thus, a pair of endless tracks protrude rearwardly from the conventional automobile or truck. The auxiliary wheels act as idlers and are mounted to the same chassis or a chassis extension frame. The tracks drive the vehicle over the snow.
Such concepts have been applied to motorcycles to convert the motorcycles into snowmobiles through the use of a conversion unit, as evidenced by U.S. Pat. No. 3,667,562 issued June 6, 1972. In that patent, the front and rear wheels of the motorcycle are simply discarded. A special tubular chassis frame is incorporated into the bottom of the motorcycle chassis and functions as an extension thereof to support a pair of endless tracks. The central drive system via chains and sprockets, is connected to the original sprocket chain drive system for the motorcycle rear wheel axle. Such conversion systems actually emasculates the motorcycle, provides major modifications to the motorcycle structure, and renders conversion time consuming. In addition, the tubular frame assembly, tracks, etc., are fairly complicated and expensive.
U.S. Pat. No. 3,318,403 to Hansen issued May 9, 1967, is suggestive of a simpler approach when modifying a motorcycle or motor bicycle to a vehicle capable of operating in the snow. In that respect, a simple clamping arrangement is employed to clamp a single ski to the front wheel of the bicycle borne by a fork assembly and operated by handle bars which are maintained in place. These means constitute a minor modification to the machine and one which can be accomplished in a matter of minutes. Further, U.S. Pat. No. 3,318,403 utilizes a rear driving assembly mounted to the rear end of the bicycle frame and taking the form of a framework supporting both the drive shaft and power sprocket, and a pair of horizontal transverse jack shafts journaled on the outermost of the paired vertical members with the lower ends of a pair of shock absorbers coupled to the pair of jack shafts. The machine incorporates a plurality of driven wheels on the outermost ends of the driven shaft with a pair of endless threads disposed on the wheels to opposite sides of the framework. While the snow bicycle is capable of functioning and moving adequately through fairly heavy snows, the components particularly at the rear of the snow bicycle are again quite complicated and involve the utilization of three open barrel or basket wheels to each side of the tubular frame assembly and the replacement of the normal rear wheel on the bicycle or motorcycle itself.
In U.S. Pat. No. 3,369,624 to Kauffmann issued Feb. 20, 1968, there is shown a vehicle capable of driving over deep snow or sand, specially formed and not as a conversion unit for an existing vehicle, which makes use of a track system mounted to each side of the vehicle at the rear ans which includes drums located forwardly of the rear wheels and swingable about the wheel axis about which the rear wheels forming endless bands pass. The bands are provided with scrapers for digging into the ground, which engage projecting tread portions of the rear wheels for forcibly driving the tracks under conditions in which the drums function essentially as idlers.
The applicant has devised a system which is based on the principles set forth in Kauffmann U.S. Pat. No. 3,369,624 for providing, to an existing three or four wheeled off-the-road vehicle, the capability of permitting the vehicle to operate in deep snow or sand or to provide additional traction when moving up steep terrain, as an attachment, which may be readily connected and disconnected to the vehicle, using a limited number of components.
It is, therefore, a primary object of the present invention to provide an improved unitary, platelike swing arm assembly for a three or four wheeled off-the-road vehicle track conversion unit which may be readily pivotably mounted to and dismounted from the rear of the vehicle, i.e., to the transmission casing, axle or chassis frame through a simple two bolt mounting system, and which utilizes a single pivot shock system for facilitating the maintenance of paired endless tracks from the rear wheels of the vehicle to auxiliary wheels mounted to the rear of the platetype swing arm to opposite sides thereof and to which the single pivot shock is centered between the auxiliary wheel axles.